Pressure control valves, such as safety relief valves, regulators, check valves, and the like, are widely used across a variety of industries and in a multitude of applications. In general, a pressure control valve may generally be used to control flow from, or within, a pressurized fluid system. Such valves may often include mechanical springs that hold a valve poppet closed against a poppet seat, thereby sealing the contained pressurized fluid within the pressurized system or regulating pressure and flow to a desired value. When the pressure in the system rises above the relief set pressure of a valve, or when flow demand of a regulator drops the discharge pressure below regulated pressure, the pressure force on the valve poppet area may become large enough to overcome the spring force acting on the valve poppet, and the poppet may lift off of the seat, allowing more fluid to exit the system and relieve pressure, or increase the flow rate. These types of valves are known to have unstable modes of operation than can cause safety critical failures of the valves.
Generally, there are two important sources of pressure losses in inlet piping for a valve that affect its operational stability. The first typical source of instability may relate to flow friction pressure losses between the pressure vessel and the valve, as higher rates of fluid flow begin to flow in the valve inlet piping after the valve opens, or in the case of a regulator, opens to a higher flow rate. As higher rates of fluid flow occur, excessive friction pressure losses may occur in the fluid travelling between the pressure vessel and the valve. Such pressure losses may cause the valve to close, and then re-open as the pressure at the valve inlet recovers after flow stoppage, resulting from the valve closing. The frictional instability may be a cyclic mechanism, with the valve closing as frictional pressure losses rise, and then re-opening once flow stops due to the valve closing.
Acoustic pressure drop at the valve inlet may be caused by acceleration of fluid exiting through the valve, which may create local pressure and flow disturbances traveling at the speed of sound in the valve supply line. The acoustic pressure drop at the valve inlet may be cyclic, with the inlet pressure remaining below the set pressure for the first half of a four-phased cycle of the lowest frequency acoustic mode (i.e., an open-closed organ pipe mode), and above the set pressure for the last two phases of the cycle. The first half cycle time duration may be the time required for the pressure/flow disturbance wave front, traveling at the speed of sound to travel from the valve to the supply tank and back. When the wave front arrives back at the valve, the compressible fluid flow effects behind the wave result in the supply line flow being larger than the valve demand flow. Therefore, this flow is decelerated at the valve inlet, causing a pressure increase at the valve inlet that rises above the valve set pressure during the last half of the cycle when the acoustic wave travels to the supply tank and back again. Since the wave front travels the distance from the valve to the supply tank four times during one cycle, the frequency of the pressure oscillation at the valve inlet is the speed of sound in the working fluid divided by four times the valve inlet pipe length.
Both the frictional and acoustic pressure drop mechanisms may be cyclic, resulting in repeated opening and closing cycles of the valve, which may cause excessive wear and/or damage to the valve. Such wear and/or damage to the valve may result in early or unexpected failure of the valve.